That was a general consensus to keep the evaporator from getting moldy. Modern cars have "afterblow" where the computer runs the fan to do this.Was there ever a time when you turned off your AC, prior to shutting off the vehicle? I did that until 10 years ago, because it was a habit I picked up from my parents....pretty sure their first 2 cars with AC (Toyota Celica and Camry), had rocker switches to turn the AC on and off. And they always turned it off, prior to rolling into wherever it was they were parking. I guess 10 years ago I learned that action is totally not necessary today.
My 1989 Mazda 323 had port-installed AC, and pushing the master switch turned it into just venting with the blower motor.